Process for preparing aluminum base alloy



United States Patent 3,234,054 PROCESS FOR PREPARING ALUMENUM BASE ALLOY Philip R. Sperry, North Haven, Conn, asslgnor to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Aug. 5, 1964, Ser. No. 387,791v 9 Claims. (61. 148-115) The present application is a continuation-impart of United States patent application Serial No. 227,000 by P. R. Sperry, filed September 28,1962, now abandoned.

The present invention relates to a process for obtaining an aluminum base alloy containing silicon and magnesium and the alloy obtained thereby. More particularly, the present invention relates to a process for obtaining an extruded aluminum base alloy as above wherein the alloy obtained therebyis characterized by improved strength characteristics while retaining the excellent characteristics desired in alloys of this type.

Various aluminum base alloys containing magnesium and silicon are well known, such as, forexample, aluminum alloy 6063 containing from 0.20 to0.60 percent silicon, from 0.45 to 0.90 percent magnesium and the balance essentially aluminum and aluminum alloy 6061 containing from 0.40 to 0.80 percent silicon, from.0.80 to 1.2 percent magnesium, from 0.15 to 0.40 percent copper, from 0.151 to 0.35percent chromium and the-balance essentially aluminum. These alloys find wide application,

for example, inthe preparation. of extruded products. That is,,products wherein. the. alloy is shaped by forcing the. heat softened alloy through. dies by pressure. These alloys arein. general characterized by a range of moderate strength properties accompanied by fair to good corrosion resistance, anodizability, formability, and weldability. In

order todevelop the strength; properties of these alloys to themaximum degree, is generally necessary-to perform costly. separate heat treatments after extrusion. Forv example, in order to develop the; full strength properties of alloy 6061, .which is the strongerof thegtwo alloys, there is required a solutionheattreatment of.970 Frforabout one hour, followed by. water quenching andthen artificial aging at 320; F. for 18 hours (T6 temper). Alloy 6061 does not have good appearanceafter anodizing. and does not resist corrosion as well,as.606-3,

The maximum, strength-properties of alloy.6063 aredeveloped by forced .air coolingafter extrusion (press quenching) followed. by artificial, aging at 350 Fjfor 8 hours. (T 6,temper).. Alternatively, for a somewhat re-..

duced strengthatlower cost, 6063 is artificiallyaged at 365. F.. for 5. hours. (T temper). The maximum strength of,. 6063 is considerably. lessthan alloy 6061.

What is desired in alloys of this type. is analloy. and

a method of manutacturewhich, would:

(1) Developat least the minimum required properties for 6063-15 by natural aging, but without any artificial aging heat treatment; and

(2) ,develop the. high strength properties of 6061 T6 simply by press quenching and artificial aging, without the need of a separate solution heat treatment.

desirable characteristics of this type of alloy, namely in particular good corrosion resistance, anodizability, appearance, forrnability, uniformly fine grain structure, and Weldability.

It is a still furtherobject of the present invention to provide a simple and expeditious process which accomplishes the aforesaid objects conveniently and at a commercially competitive cost.

Further objects and advantages of the present invention are apparent hereinafter.

In accordance with the present invention, it has now been found that the foregoing objects and advantages as well as others may be readily accomplished. Briefly, the process of the present invention comprises:

(a) Providing an aluminum base alloy containing from 0.60 to 0.90 percentsilicon, from 0.40 to 0.60 percent magnesium and the balance aluminum, wherein said silicon and magnesium are uniformly distributed throughout the said alloy, preferably by an elevated temperature homogenization treatment;

(b) Heating said alloy to a temperature of at'least 970 F.;

(c) Holding said alloy at said temperature of at least 970 F. for at least 2 minutes;

(d) Extruding said alloy at a temperature in excess of 950 F., i.e., before the surface temperature of the billet has dropped below 950 F; and

(e) Rapidly cooling said extruded alloy to a temperature of at least 350 F. in at most 4 minutes.

Ithas been found that the alloy treated in accordance with the foregoing process develops criticaly improved properties. Upon natural aging after extrusion it develops properties exceeding the minimum guaranteed for 6063- T5. In addition, however, it has been further found that still greater improvement is obtained when the alloy is thermally artificially aged subsequent to the rapid. cooling step.

Thus, the improved. alloy of the present invention is a high strength extruded aluminum base alloy containing from 0.60 to 0.90 percent silicon, from-0.40 to 0.60 percent magnesium, and the balance aluminum, wherein the silicon and magnesium are retained in solid solution, said alloy being in the extruded condition. minimum strength properties of the extrusion of the-present invention are: tensile strength 26,000 p.s.i.; and yield strength 16,000 p.s.i.

The alloy to which the present invention relates is an aluminum base alloy-containing from 0.60 to 0.90- percent silicon, fromj0.40 to 0.60 percent magnesium and the balance aluminum. Preferably when the alloy is in the T-42 temper (naturally aged) it contains from 0.75 to 0.85 percent silicon and from 0.50 to0.60 percent magnesium. Preferably when the alloy is in the T-5 temper (artificially aged) it contains from 0.70 to 0.85 percent silicon and0.45 to 0.60. percent magnesium. Preferably the total magnesium plus silicon content should range from 1.3 to 1.5 percent and the preferred ratio of silicon to magnesium in the aluminum alloy is from 1.30:1 to 1.5: 1, with an optimum total magnesium plus silicon content being about 1.4. percent in conjunction with an optimum silicon to magnesium ratio of 1.4:1. found that the foregoing composition is preferred and provides the optimum characteristics of strength, anodizability, corrosion resistance, formability and extrudability.

Naturally, the presentinvention contemplates conventional impurities common for alloys of this type. This is important since it indicates that the improved properties of the alloys in the present invention are obtainable with normal commercial impurity materials. For example, normal impurities comprise: 0.35 percent maximum iron; 0.10 percent maximum copper; 0.10 percent maximum manganese; 0.10 percent maximum chromium; 0.10 per- Generally, the

It has been cent maximum zinc; 0.10. percent maximum titanium;-

and 0.05 percent maximum each of other elements, the total of which is a maximum 0.15 percent.

Themanner of melting and casting the alloy is not especially critical and conventional methods of melting and casting may be conveniently employed. Before the process of the present invention is performed, however,

it is important tounifor'rnly distribute the silicon and 7 magnesium throughout the matrix of the alloy. This may be done many desired mannenifor example, it may be done preferably by a homogenization heat treatment sub- 7 sequent to. the casting operation. In fact, the preferred 20 hours. In the preferred 'embodimenhthe homogenization treatment is followed by cooling'to room temperature in any desired manner.

The cooling of the cast ingots subsequent to the homogenizationtreatment is normally rather slow'because of follow the homogenization treatment. In accordance with the present invention, this precipitated material must be velop full strength and "hardness in the present alloy;

' from '15 ,minutes to 9 hours at a temperature of from the large mass of material involved. 7 Consequently much of the soluble alloying constituent necessarily is precipi- I tated out of solution during theslow cooling which. must '25, completely redissolved prior to extrusion in order to de-.

air cooling using appropriately .placedfansin order to provide some continuous replacement ofair.. In sections in excess of A of an inch in thickness, it is generally, desirable to obtain a suitable cooling rate by passing the extrusion through a water spray quench, if this can be done without excessive distortion of the. extruded shape.

The resultant: as extruded 1'alloy,.thus is a moderate strength extruded aluminum :base T alloy and has been found to have excellent-physical properties, such as'formability, weldability, corrosion resistance, and anodizability.

obtained subs'equentto the rapid cooling step by thermally;artificially aging the extrusion.- The -preferred mannerof this artificial Iagingis. to maintain the extrusion for 200 to. -410"F. and preferablyat about 350 'F. and

from 4 to '8hours.- With the foregoing artificial aging *treatment the .alloy of the present: invention attains strength properties equivalent to those. of the more expensive alloy 6061' and fact exceeds by far the strength properties of :alloy, 6063 in the ,T5 or artificially aged 7 condition; These advantages are obtained withno sacrif Naturally, where the silicon and magnesium are dissolved I as wellias uniformly distributed throughout the matrix of l the alloy, it is unnecessary to redissolve these materials However, it is judicious to perform the redissolving step in order to insure the dissolution of all ;of these materials.

In accordance with the present invention-,therefore. the:

alloy should be heated to a temperature of at least 970" F. and held at-tnat temperature for at least 2 minutes.

The temperature 970 F. is the solution temperature. for

the soluble 'magnesium' and silicon components and the:

period of at least 2 minutesg-is normallythe minimum- The minimum time of treatmentis notespecially' critical.

It is noted inithis regard that optimum properties are; developedonly if all of the alloy is-retained at at least? fice in the other desirable characteristics ofthis typegof allow-such as,zfor example, extrudability, anodizability,

finishing characteristics, corrosion 'resistance or weldabil l ity.. ,In ;addition,1the advantages. of, the present invention have been obtained without, a separate solution heat treatelongatioin,ghence ductility; Thus the present-alloy otters an extremelyi. versatilerrange of properties heretofore un-' attained in an inexpensive alloy. 1

For exarnple,.when the alloy of the-present invention .is, artificially aged :at. 310;:F3 for/2. hours, "it will have; yield and mlt-imate strengthssomewhat higher thanthosefor alloy16063 in theyrTS' jo'r artificially .aged condition;

1 while F its elongatiodwill be *l8ipercent'instead of the 9-70", F. and at least-2 minutes, in other words,-op t imt1m results 'Will be obtained only' if the temperature at-the' centerof-the billet reaches 970' For higher andis kept from falling below- 970 F.-for z min'utesjprior to ex-' trusion. i

Subsequent to the-.heating-and ,holding step the extru-" sion billet of the desired alloy is inserted 'into theiext'ru-i,

sion press beforethe,surfaceternperature'has droppedbe-fl J Naturally, 'inzviewof the foregoing, the .alloy should'not 12 percent'typical of alloy 6063 jinxthe. .TS orilart'ificially I aged condition. This characteristic w o-uld al-low more. forming to be-done on the alloy of the .present inven: tion: thancn alloy: 6063-T5 while? maintaining a better" 7 than average gstrengthi'level'.

In addition thegalloy of the'pi esent invention hasother highlyabeneficial andrdistingu-ishirig characteristics. The alloy of the present invention shows distortion upodbompletion of extrusion; and therefore the.subse-.-.- 'quent straighteningrequired is qui-telsmall; iwhereas 6061 distorts appreciably andirequires fairly extensive Isu'bsebe cooled below 950 F. prior to extrusionbut should be extruded directly after-the heating andholding' steps. The upper temperatureis' dependent upon surface ap-.-

pearance and temperature effects on the extrusion tools; generally, however, a temperature of-less than 1050 F.

is used. 7

Subsequent to extrusion'jit is critical that the extruded.

alloy berapidly cooled in order to eventuallyiobtain the;

The effect of the rapid maximum strength i properties. cooling is to retain-the solublemagnesium and silicon constituents in solid solution. Ithas been found that the critical cooling step is to bring the extruded alloy down:

to a temperature of 350 F. or lower in 4 minutes or' less. Naturallylit is preferred that the alloy be cooled more rapidly than the' foregoing minimum'cooling rate.

More rapid cooling gives better ductility combined .with

economize-s thesjextrusioni operation and? also permits better dimensional control of complex; shapes. 1 In, addie; V :tion, the presentr'alloy has: good properties on porcelain; enameling, superior to 113116 ;convent-iona.lly'; used 6063; In addition, the electrical characteristics of the p'resent alloy are good, ii.e., the, present alloy 1is a high. strength, moderate conductivity alloy, For example, the present alloy haslan electrical ,eonductivityof 50 percentat peak hardness-equivalent to. 6061-T6 wh-ioh'hasia con-- ductivity e f-43 percehtxIACSf Alloy 6063 has consider ably lower hardness.

The present i invention will be; more readily apparent from a consideration of the fol-lowing illustrative ex-h,

amples.

' EXAMPLE I i marized at follows.

It is further noted that the; resultant alloys obtain. improvedstrength levels without degradation of the afore-. 1 mentioned desirable characteristics of alloys of thisgtype.

A -still further "and fact surprising ,finding ofiithe. present .inventionis the level. of additional improvement quent' straighteningn Thisadvantage-of the present alloy minutes. The average pouring temperature was 1360 F. The average casting speedwas per minute and the metal head was maintained between 2.5 and 3";

The composition of the alloy prepared was as follows: 0.55 percent magnesium; 0.82 percent silicon; 0.16 percent iron; 0.02 percent zinc; and traces of. copper, manganese and chromium.

EXAMPLE II The silicon and magnesium in thecast ingots were uniformly distributed. throughout the matrix by the following homogenization procedure. The. ingots were heated so that the entire furnace load. reached a temperature exceeding 970 E. within the first 8 hours. They were then heldfor an additional 6 /2 hours, during which time. no port-ion of the furnace load exceeded 1095 F. Finally, theentire load was removed from th furnace and cooled in air which took about 6 hours.

EXAMPLE III The ingots prepared in accordance with Examples I and II were subjected to three different types of treatments, identified below as Treatment A, Treatment B and Treatment C;

Treatment"A.-The ingots were placed in a gas-fired, continuous feed furnace maintained at 1000 F. and retained therein for 20 minutes. Upon exiting from the furnace, the surface of the alloy was allowed to cool to 960 F. The ingots werethen extruded, with the surface temperature being 930 to 990 F. upon exiting from the extrusion press, followed iby'rapidly cooling to room temperature, with a temperature of 350 F. being attained in 4 minutes or less.

Treatment B.The ingots were placed in an electrical induction heater set to give a heating time of /2 minute at 9901000 F. Upon exiting from the heater the surface temperatures of the billets was all-owed to cool to three different levels as follows:

Treatment B1, cooled to 920 F.; Treatment B2, cooled to 950 F.; and Treatment B-3, cooled to 980 F.

The ingots were then extruded, with corresponding surface temperatures obtained upon exiting from the extrusion press as follows:

B-l, surface temp, 900'970 F;

B2, surface temp, 9401000 F.; and

B-3, surface temp, 950-1020 F.

Following extrusion all alloys were rapidly cooled to room temperature, with 350 F. being attained in 4 minutes or less.

Treatment C.-In=gots were treated in a manner after Treatment B, except that the electrical induction heater was set give a heating time of 2 minutes and upon exiting from the heater the surface temperature of the billet was allowed to cool to a temperature not below 950 F.

EXAMPLE IV The properties of the extrusions obtained in Example III were determined as follows: the tensile strength was determined; the yield strength at 0.2 percent offset; and elongation in 2 inches. The results are given in the following table. These are compared with the minimum properties of the comparable alloy 6063-T5.

The foregoing shows that in the treatment conditions of Example III, Treatment A, the heating time of 20 minutes was long enough to guarantee that all of the magnesium and silicon would be taken back into solution so that the minimum strength properties of alloy 6063-T5 are readily exceeded. However, the treatment conditions of Example III, Treatment B-l, B2 and B-3, namely a heating time of /2 minute, was not long enough to guarantee that the minimum will be exceeded. But the treatment conditions of Example III, Treatment C was sufficient, namely 2 minutes.

In addition to exceeding the minimum strength characteristics of alloy 6063-T5, the alloys of the present invention have excellent elongation which enable them to be more readily formed than 6063T5.

A further, and in fact quite surprising characteristic, Was that the alloys of the present invention were found to have superior punching and blanking characteristics than 6063-T5. This is quite surprising in view of the higher ductility of the present alloy.

EXAMPLE V The alloys treatedin the manner of Examples I, II and III were artificially aged under varying conditions and tensile strength, yield strength and elongation determined. The results are'com-pared with the minimum and typical properties of 6061-T6 and 6063-T5'. The results substantiate that the. alloy of the present invention is comparable in strength characteristics to the expensive 6061- T6 and far superior to 6063-T5. The results are given in the following table.

In addition, the alloys of the present invention were formed to have extrudability comparable to or slightly better than 6063, and far better than 6061, which enabled complex shapes to be extruded with a minimum of distortion and good demensional control.

EXAMPLE VI The following additional properties of the alloys of the present invention were evaluated:

(1) Corrosion resistance-Either the natural or artificially aged alloy of the present invention were found to be superior to 6063 or 606 1 as determined by immersion in a corrosive environment, e.g., sea water.

(2) Anodizability.-Either the natural or artificially aged alloy of the present invention were found to have a pleasing and uniform appearance upon etching and anodizing by standard anodizing procedures; and

(3) Weldability.-Either the natural or artificially aged alloy of the present invention were found to be readily weldable in a manner comparable to 6061 or 6063.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

7. What is claimed is: 1. The process which comprises:

(a) providing an aluminum base alloy consisting es- I sentially of from 0.60 to 0.90 percent silicon,vfrorn t 0.40to 0.60 percent magnesium and the balance.

aluminum,*wherein said silicon and magnesium are uniformly distributed throughout said alloy and are dissolved therein; 7

(b) extruding said alloy at a temperature in excess of 950: F.; and

of at least 350 F. in at most 4 minutes. 2. The process which comprises:

(a) providing an aluminum, base alloy consisting cs1 sentially of from 0.60 to 0. 90 percent silicon, from 0.40* to 0.60 percent; magnesium and thebalance aluminum, wherein said silicon and magnesium are} 3. A process according to claim 2 .Where said silicon. and magnesium are uniformly distributed'throughout the said alloy by homogenizing at-a temperature of from 970 to 1100 F. for from 4 to 20 hours.

10 (c) rapidly cooling'said extruded alloy to a temperature 8E 4. A process according .to claim 2 wherein after said' rapid cooling said alloy is thermally artificially aged. 5; A process according to claim 4 wherein said artificial aging is from 15 rninutesto 9 hours at1200'to 410 F.

6.; A, process according to claim 4 wherein said alloy is artificially aged at.about.3509 F. for from .4 m8 hours.

7. A process according to claim 2 whereimthe total silicon and magnesium content in saidaluminum alloy is I from 1.3 to 1.5 percent. 7 a

8."A process according to claim 2 wherein:the ratio 'of'silicon to'magnesiu'rn inisaidaluminum alloy is from 9. A process according to claim 12 wherein the alloy 7 contains in addition 0.35 percent maximum iron; 0.10 percent maximum copper, 0.10 percent-maximum manganese,

0.10 perceut'maximum chromium; 0.10 percent maximum zinc, 0.10pe rcent maximum titanium and 0.05 "percent maximum each of:other,elements totaling a:.maximum 0.15 percent;

References Cited by theiExarninei- I UNITED ST TES PATENTS 1,472,739 10/1923 Archer et al. v 141832.5 3,019,144 1/1962 'Murphy et al. 1484121 DAVID; L. RECK; ,Primar y Eraminen...

YF. SAITO, fissiStant Examiner. 

1. THE PROCESS WHICH COMPRISES: (A) PROVIDING AN ALLUMINUM BASE ALLOY CONSISTING ESSSENTIALLY OF FROM 0.60 TO 0.90 PERCENT SILICON, FROM 0.40 TO 0.60 PERCENT MAGNESIUM AND THE BALANCE ALUMINUM, WHEREIN SAID SILICON AND MAGNESIUM ARE UNIFORMLY DISTRIBUTED THROUGHOUT SAID ALLOY AND ARE DISSOLVED THEREIN; (B) EXTRUDING SAID ALLOY AT A TEMPERATURE IN EXCESS OF 950*F.; AND (C) RAPIDLY COOLING SAID EXTRUDED ALLOYY TO A TEMPERATURE OF AT LEAST 350*F. IN AT MOST 4 MINUTES. 